Spinal vertebral implant and methods of insertion

ABSTRACT

A spinal vertebral implant includes a substantially rectangular shaped base section made from a solid piece of bone. A nose section extends integrally from the substantially rectangularly shaped base section and preferably has a generally tapering shape to foster entry between adjacent vertebrae. The nose section tapers distally and inwardly from the base section to form a generally pointed or rounded distal tip portion and comprises a solid piece of bone. Serrated sides assist the implant in gripping adjacent upper and lower vertebrae and in being maintained therebetween. The serrated sides are angled in a manner that encourages the implant to be placed between the vertebrae and locked therebetween upon such placement. First and second implants may be placed into respective left and right sides of an intervertebral space. A method for placing one or more implants between the adjacent vertebrae comprises forming a slot configured to receive an implant and inserting the implant into the slot. Each slot is preferably formed from an upper slot portion and a lower slot portion in the posterior portion of adjacent upper and lower vertebrae, respectively. Instruments for performing the method include osteotomes, impactors, and spacers.

BACKGROUND OF THE INVENTION

[0001] 1. The Field of the Invention

[0002] This invention relates to spinal vertebral implants and methodsand instruments for inserting the implants between spinal vertebrae inorder to achieve spinal fusion.

[0003] 2. The Prior State of the Art

[0004] When tissues between spinal vertebrae, also known asintervertebral disks, become herniated or otherwise injured, the diskscan compress against nerves associated with a particular location on aspinal column. Such injuries are common in the lumbar vertebrae, forexample, and can cause extreme pain to a patient suffering from suchinjuries.

[0005] One treatment common among medical providers to treat suchinjured intervertebral disks is a spinal fusion. In typical spinalfusion procedures, a portion of a vertebral disk or the entire vertebraldisk is removed from between adjacent upper and lower vertebrae and theupper and lower vertebrae are fused to form a single spinal structure.The fusion of the vertebrae can alleviate the pain and discomfortassociated with injured disks and frequently does not result insignificant loss of bending capability.

[0006] A variety of different treatment modalities have been developedto perform such spinal fusions. Examples of typical treatments includethe use of a spinal implant placed between two adjacent vertebrae.Typical implants include those made from bone, often harvested from acadaver, for example. Following the removal of the intervertebral disk,the spinal implant is placed between the vertebrae and fuses over timewith the vertebrae, eventually forming a single fused member. Typicalimplants can also comprise a metallic material, for example.

[0007] A variety of different approaches have been developed to useimplants to achieve spinal fusion. For example, one approach employs acage-like metallic structure in which fragments of bone are placed. Thecage is mounted between adjacent vertebrae and is designed to maintaindistraction between vertebrae, thus maintaining the vertebrae a desireddistance apart from each other. The bone fragments foster fusion betweenthe adjacent vertebrae. However, the cage-like structures merely act asdistractors and do not fuse between the vertebrae. Instead, only thebone fragments foster fusion between the vertebrae. Thus, the space usedby the cage is not used to foster bone growth and fusion. Furthermore,if bone growth does not occur through the holes for any reason, theimplants merely serve as distractors, that is, placeholders thatmaintain spaces between adjacent vertebrae, rather then fostering fusiontherebetween. The use of metal cages also introduces a foreign objectinto the disk space where fusion is to be obtained.

[0008] Other implants comprise harvested bone without a cage member.Typical such implants include implants comprising first and second bonepieces coupled together, for example. However, such coupled pieces canfail to fuse to each other, or can form a false joint which caneventually result in decreased fusion or the lack thereof.

[0009] There is therefore a need in the art for an improved spinalfusion implant that can be mounted between adjacent vertebrae andachieve fusion therebetween. There is also a need in the art for animproved method for placing spinal fusion implants between adjacentvertebrae. There is also a need in the art for instruments capable ofachieving improved methods for implanting spinal implants.

SUMMARY OF THE INVENTION

[0010] The present invention relates to a spinal vertebral implantcomprising a substantially rectangular shaped base section comprising asolid piece of bone. A nose section extends integrally from thesubstantially rectangularly shaped base section and preferably has atapering shape to foster entry between adjacent vertebrae. The distaltip of the implant can be pointed or rounded, for example. The preferrednose section tapers distally and inwardly from the base section to formthe distal tip portion and comprises a solid piece of bone. The implantis preferably cut from a longitudinal section of a long bone of a humancadaver.

[0011] Serrated sides assist the implant in gripping adjacent upper andlower vertebrae and in being maintained therebetween. The serrations arepreferably angled in a manner that encourages the implant to bemaintained between the adjacent vertebrae upon placement therebetween.The serrations grip and can impact into the adjacent vertebrae. Thus,the serrations assist in maintaining the implant tightly within theintervertebral space. First and second implants are generally placedinto respective left and right sides of an intervertebral space unlessthe patient suffers from scoliosis or another particular condition ortreatment modality applies, in which case it may be possible to use onlyone implant. In yet another embodiment, more than two implants areimplanted, however, at least two implants are generally preferred.

[0012] A method for placing one or more implants between the adjacentvertebrae comprises forming one or more angled slots located inposterior portions of the vertebrae and configured to receive animplant. The implant is inserted into the angled slot and then furtherinserted between the vertebrae. Each slot is preferably formed from anupper slot portion and a lower slot portion in the respective upper andlower vertebrae. Each of these slot portions may be formed in a varietyof different manners, such as by cutting or crushing a posterior portionof the edge of adjacent vertebrae. Once the implant is initiallyinserted into the slot, the implant can be pressed further between thevertebrae, thereby forcing a tightly inserted fit between the implantand the adjacent vertebrae.

[0013] In one embodiment, one or more slots extend from the posteriorends of the vertebrae at least approximately one third to approximatelyone half the distance between the anterior and posterior ends of theupper and lower vertebrae, although a variety of differentconfigurations are available.

[0014] In one embodiment, each of the upper and lower slot portions areangled with respect to the longitudinal axis of the upper and lowervertebrae such that the placement of rectangular implants within theslots and the subsequent compression of the posterior portions of thevertebrae results in a desired level of lordosis. Through the use of theangled slots and a rectangular piece of bone, the anterior portions ofthe vertebrae are distracted or spread apart, thereby producinglordosis.

[0015] Instruments specifically designed to assist in the formation andultimate configuration of the slots include, for example, (i) osteotomesdesigned to form a slot having a size substantially corresponding to theimplant; (ii) an impactor designed to substantially mate with theproximal portion of the implant and drive the implant between adjacentvertebrae; (iii) and spacers having varying sizes that are designed toassist in enlarging the space between adjacent vertebrae and provide aspace for the implant. Optionally, other instruments are employed tocrush the cortical posterior bone portions. These and/or otherinstruments and one or more implants may form a kit for filling anintervertebral space with materials enabling fusion of upper and lowervertebrae. Other components of the kit may include bone fragments to beplaced in the slots and the remaining portion of the intervertebralspace to completely fill in the intervertebral space. Mechanicalfixation devices such as pedicle screws and related instruments may alsobe used to secure the vertebrae in place and apply compression to theposterior region following the placement of the implant between adjacentvertebrae, thereby achieving and maintaining a desired level oflordosis.

[0016] The preferred longitudinally cut implant can be contacted by aninstrument such as an implant impactor with significant force at aposterior end of the implant without splitting or crushing the implant.This is in part because the direction of the impact from the implantimpactor is in a linear relationship with the orientation of the grainof the bone forming the implant, rather than perpendicular to the grainof the bone forming the implant.

[0017] Also in light of the use of the cut slots, the implanted implantand associated bone fragments become incorporated more readily into thespine as part of the fusion for two reasons. First, the slots offerincreased surface area. Second, the cutting of the slots causes the boneto more readily fuse.

[0018] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by the practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other objects and features of the presentinvention will become more fully apparent from the following descriptionand appended claims, or may be learned by the practice of the inventionas set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order that the manner in which the above-recited and otheradvantages and objects of the invention are obtained, a more particulardescription of the invention briefly described above will be rendered byreference to specific embodiments thereof which are illustrated in theappended drawings. Understanding that these drawing depict only typicalembodiments of the invention and are not therefore to be considered tobe limiting of its scope, the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

[0020]FIG. 1A illustrates a perspective view of a spinal fusion implantof the present invention;

[0021]FIG. 1B illustrates a side view of the spinal fusion implant ofFIG. 1A;

[0022]FIG. 1C illustrates an opposing side view of the spinal fusionimplant of FIG. 1A.

[0023]FIG. 1D illustrates a top view of a spinal fusion implant of FIG.1A, the opposing bottom view being shown in FIG. 1E;

[0024]FIG. 1F illustrates a view of the rear (i.e., proximal) end of aspinal fusion implant of FIG. 1A with phantom lines illustrating sideserrations.

[0025]FIG. 1G illustrates a view of the tapering front (i.e., distal)end of a spinal fusion implant of FIG. 1A with phantom linesillustrating side serrations.

[0026]FIG. 1H illustrates a view of the rear (i.e., proximal) end of analternative spinal fusion implant from that of FIG. 1A that does nothave a concave medullary canal portion therein.

[0027]FIG. 2 illustrates the spinal fusion implant of FIGS. 1A-1Finserted between the vertebrae of a patient. A portion of a vertebralcolumn is shown with side portions of the upper and lower vertebraedepicted in a cutaway view.

[0028]FIG. 3 depicts a cutaway, rear view of the column of FIG. 2showing first and second spinal fusion implants inserted betweenadjacent upper and lower vertebrae. FIG. 3 is merely a depiction forpurposes of illustration only and does not show the neurologicalelements with the spinal canal, for example.

[0029]FIG. 4A illustrates the desired location of first and second slotsbetween spinal vertebrae. The right slot is shown in a phantom view.

[0030]FIG. 4B illustrates the creation of first and second lower slotportions on a lower vertebra using a box osteotome of the presentinvention. The slot portions are cut at an angle with respect to alongitudinal axis “L” of the top portion of the lower vertebra. Anexample of an implant is shown in a phantom view placed in a right slot.

[0031]FIG. 4C illustrates the creation of upper and lower slot portionsto form a collective slot using an alternative instrument of the presentinvention.

[0032]FIG. 5A illustrates the use of a spacer to create additional spacebetween upper and lower vertebrae following the creation of the slot(s)depicted in FIGS. 4A-4C. Such space can be created through compressionof cancellous bone in the upper and lower vertebrae and/or bydistracting the upper and lower vertebrae.

[0033]FIG. 5B illustrates the placement of additional bone fragmentsinto the intervertebral space following the procedure of FIG. 5A.

[0034]FIG. 5C illustrates the placement of a spacer into theintervertebral space following the procedures of 5A and/or 5B.

[0035]FIG. 6A illustrates the insertion of the spinal implant of FIGS.1A-1F using an impactor of the present invention.

[0036]FIG. 6B illustrates first and second inserted spinal fusionimplants with bone fragments shown surrounding the inserted implants ina cross sectional view of a vertebral column to fill the intervertebralspace with bone material comprising bone fragments and implants.

[0037]FIG. 6C illustrates upper and lower vertebrae with an implanttherebetween in a manner that achieves a desired lordosis by mounting aproximal portion of the implant in posterior slot portions, mounting adistal portion of the implant in an anterior portion of theintervertebral space and affixing a mechanical fixation device toposterior portions of the vertebrae to achieve posterior compression.

[0038]FIG. 7A demonstrates the final coupling of a mechanical fixationdevice to the spinal column to maintain the desired compression ofvertebrae in place following the placement of implants between multiplevertebrae.

[0039]FIG. 7B demonstrates a variety of fused vertebrae, as can beachieved through the use of the system, method and tools demonstrated inFIGS. 1-7A.

[0040] FIGS. 8A-9 demonstrate a series of instruments useful in a kit ofthe present invention as depicted in the foregoing described Figures andthe discussion relating thereto.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] The present invention is directed generally to spinal vertebralimplants that are configured to foster bone fusion between adjacentupper and lower spinal vertebrae, and methods and instruments forinserting the implants. Certain goals of the procedure includedecompressing neural elements and to provide the optimum environment forfusion in a normal bone-neural configuration. This includes restoring anoptimal intervertebral space height and a normal lumbar lordosis.

[0042] With reference now to FIGS. 1A-1F, an example of a spinalvertebral implant used according to the present invention will now bedescribed. FIG. 1A shows a perspective view of an implant 10. Implant 10has a base section 12 and a nose section 14 extending integrally frombase section 12. Base section 12 preferably has a length that is greaterthan the height and thickness thereof. Nose section 14 has a generallytapering shape and extends integrally from the base section and tapersdistally and inwardly from the base section to form a generally pointedor optionally rounded distal tip portion.

[0043] Generally, the implant 10 comprises a solid piece of bone thatmay be termed a “bone block”. The spinal vertebral implants of theinvention can generally be formed from bone blocks cut from frozenallograph femur or tibia, for example. The implants are preferably bonetaken from a longitudinal section of the bone. In other words, thelongitudinal axis of implant 10 is parallel to the longitudinal axis ofthe bone from which the implant is taken. The grain of the implant andbone is also parallel to the longitudinal axis of the bone.Consequently, as the implant is impacted into the intervertebral spacewith an implant impactor contacting the posterior end 21 of the implant,the implant is not damaged, but can withstand significant impact forces.

[0044] Also in a preferred embodiment, as shown, the height “H” of theimplants is significantly greater than the thickness “T” thereof,allowing maximum vertebral distraction (i.e., forcing vertebrae apartfrom each other) with minimal nerve root retraction. This dynamicenables maximum distraction of the vertebrae without requiring thepractitioner to injure nerves while inserting the implant. Acylindrically shaped implant, on the other hand, generally has the sameheight and thickness, requiring more nerve retraction because of thethickness of the implant and increasing the risk of nerve injury.

[0045] The implants of the present invention are driven into preformedslots in the intervertebral space to distract the vertebrae, as will bediscussed in greater detail below.

[0046] Also as shown in FIG. 1A, base section 12 has first and secondsides 16, 18. At least one of the sides and preferably both of the sideshas a plurality of serrations 20 therein. Serrations assist the implant10 in remaining between adjacent vertebra when driven therebetweenthrough the use of one or more instruments as described hereinbelow. Theserrations are angled to allow ready insertion in the distal, anteriordirection (see arrow 40 in FIG. 2) and prevent retraction of the implantin the proximal, posterior direction. Thus, the implanted implantsremain between adjacent vertebrae.

[0047] As shown in FIGS. 1F-1G, implant 10 further comprises an optionalcanal portion 22, extending along the longitudinal axis of the base andnose sections. Canal portion 22 is a portion of the substantiallycircular medullary canal of the bone from which implant 10 is harvested.It can function to provide additional space for a bone graft to form.However, canal portion 22 is not necessary to the function of theimplant.

[0048] It will be appreciated by one skilled in the art in light ofdisclosure herein that although it is possible to use a canal 22, it isalso possible to achieve the objects of the present invention withoutthe use of a canal portion, such as by employing a flat implant 10′, asshown in FIG. 1H, which demonstrates a posterior, proximal portion of animplant 10′ and shows serrations 20′ in phantom lines. Implant 10′ has athickness “T”. For example, if the bone from which the implant 10 isharvested is sufficiently large, the canal portion 22 may be omittedentirely. In smaller bones, the presence of a medullary canal portionmay be inevitable because a minimum implant thickness must bemaintained.

[0049] Also as shown, in one embodiment, nose section 14 is preferablysubstantially shorter than base section 12. However, in anotherembodiment, the nose section is the same length or longer than the basesection. A variety of other shapes and configurations are also possible.

[0050] Referring back to FIG. 1A, in one embodiment implant 10preferably has a length in the range of about 20 mm to about 40 mm, morepreferably about 26 mm to about 34 mm, and most preferably about 30 mm;a height “H” in the range of about 8 mm to about 25 mm, more preferablyabout 12 to about 20 millimeters, and most preferably about 16 mm; and athickness “T” preferably in the range of about 4 mm to about 15 mm, morepreferably about 8 mm to about 12 mm, and most preferably about 10 mm.However, a variety of sizes are available depending upon the shaperequired for a particular procedure and the size of the patient.

[0051] Implant 10 preferably comprises a solid piece of bone. In oneembodiment, implant 10 consists of a solid piece of cortical bone.Cortical bone is preferably employed because of the hardness thereof.Cortical bone is typically found in the long bones of a human cadaver,such as the human tibia and femur. Depending on the size of the cadaverfrom which the implant is harvested, however, other bones, such as thehumerus, may also function adequately. In contrast, cancellous bone issoft and collapses under less strain.

[0052] Another aspect of the present invention is the manner in whichthe bone is cut from the long bone. Unlike other methods, which cut thelength of an implant transversely across the femur, the presentinvention preferably incorporates implants that are cut longitudinallyalong the longitudinal axis of the femur. In other words, thelongitudinal axis of implant 10 is parallel to the longitudinal axis ofthe bone from which the implant is cut. This method of cut has a numberof advantages. First, it provides for longer implants that can be cutfrom the femur or other bone. Second, depending on the bone diameter andcortical bone thickness, the longitudinal cuts allow multiple boneimplants to be harvested form a single cross section of a femur or otherbone. Nevertheless, a variety of different types of bone and cuttingmethods thereof may be employed. In addition, as mentioned, impactagainst the posterior end 21 of implant 10 does not damage implant 10.

[0053] Thus, in one presently preferred embodiment, base section 12 andnose section 14 comprise a piece of cortical bone harvested from alongitudinal section of a bone such as the femur, for example. The bonecan also be harvested from a variety of other locations, such as thetibia or humerus. Each harvested implant will generally not beidentical, due to the varying nature of cadavers, and thus the shape andshading of implant 10 is merely exemplary. However, they can each bemachined to achieve the desired dimensions.

[0054] There are numerous advantages to the spinal vertebral implants ofthe present invention. Many of the advantages derive from the shape ofthe implants. For example, the tapering nose 14 enables a practitionerto drive the implants 10 readily into an intervertebral space, using thenose 14 to wedge in between the adjacent vertebrae.

[0055] A further advantage of the shape is the way the serrations act asstops and grasp adjacent bone portions of the vertebrae. The serrationson upper side 16 and lower side 18 “grab” the upper vertebrae 30 and thelower vertebrae 32. This helps immobilize the implant in place, enablinga better bone fusion and increased stability. The serrations are angledwith an angled portion 24 of a given serration oriented anteriorly and aflat portion 26 thereof oriented posteriorly (see FIG. 1C) to assist thepractitioner in driving the implant into the intervertebral space andpreventing the implant from being pressed out of the space. Theserrations preferably press fit in a tight fitting relationship withadjacent upper and lower vertebrae, as shown in FIG. 2.

[0056] Another advantage is the generally rectangular shape of theimplant body, which enables the implant to fit conveniently betweenadjacent vertebrae and enhances fusion and distraction between the upperand lower vertebrae. The tight fit of the implant body in theintervertebral space also maintains the distraction of the disc spaceuntil the fusion completes.

[0057] The implant material is advantageous in that the solid nature ofthe implant 10 fosters bone growth and the use of natural bone enablesthe implant 10 to fuse to the upper and lower vertebrae as well as toadjacent bone fragments placed within the intervertebral space tocompletely fill in the space with bone material. The use of bone in thefusion encourages bone growth. Bone will grow from adjacent bone sourceswith available blood supply. Over time, bone from the vertebrae willgrow into the implant, incorporate it and completely replace the implantwith a patient's bone. Thus, the implant, bone fragments placed in theinvertebral space as discussed below and the upper and lower vertebraeall fuse together from the stimulated bone growth. It is an advantage ofthe present invention that the use of bone allows not only the bonefragments, but the bone implant itself to become incorporated as part ofthe final fused spine.

[0058] Further, because the implant is one solid piece, it is strongenough to be driven in and maintained between vertebrae withoutstructural failure. Finally, bone will incorporate naturally into thebone fusion, whereas metal will not.

[0059] With reference now to FIGS. 2 and 3, examples of placement ofimplant 10 will now be described. As shown, it is preferred that firstand second implants 10 a, 10 b be placed between upper and lowervertebrae 30, 32. Side portions 31, 33 of respective upper and lowervertebrae 30, 32 are partially cut away in FIGS. 2, 5b and 5 c (seehatching), in order to completely illustrate the placement of implant 10between the vertebrae.

[0060] It is preferred to drive implant 10 between adjacent vertebrae30, 32, such that implant 10 achieves a desired level of distraction ofthe anterior portions of vertebrae 30, 32. By driving nose section 14between the adjacent vertebrae 30, 32, implant 10 is forced between thevertebrae and thereby accomplishes a tight fit therebetween, therebyfostering and encouraging greater fusion and preventing the implant frombeing forced out of the intervertebral space.

[0061] It is preferred that a small anterior portion of theintervertebral disc 34, known as an annulus 34 (as well as the anterior,longitudinal ligament), be left remaining between the adjacent vertebraeduring the surgery such that a desired distraction is achieved and tomaintain bone fragments placed within the intervertebral space. See alsoFIG. 6B. Annulus 34 also provides stability while the bone fragments andimplants fuse in the intervertebral space. It also acts as a tensionband, which maintains tension between the vertebrae and helps toimmobilize the vertebrae. As shown at arrow 40, implant 10 is preferablyinserted from the posterior section of the spinal column in the anteriordirection. Upper and lower slot portions 36A, 36B which combine to forma single slot 36 into which implant 10 is placed are partially shown inFIG. 2.

[0062] With reference now to FIG. 3, first and second implants 10A, 10Bare shown in respective slots 36, 38 (see also FIG. 4A). In a preferredembodiment first and second implants are so maintained between the discssuch that the two implants simultaneously provide fusion potential andbalance the vertebrae thereon.

[0063] Also as shown in FIG. 3, the convex portion of each implant 10 a,10 b is placed medially. This is advantageous because it places thesmooth portion of the implant to closest to the nerve, therebyprotecting the nerve. Even though preferably retracted, the nerve canslip. Thus, the smooth, convex portion is preferably placed as shown.

[0064] One method of inserting one or more implants 10 according to thepresent invention will now be described in additional detailhereinbelow. Only those steps that are instructive to the methods of thepresent invention will be discussed herein. Those procedures notdiscussed herein are well known in the art and do not require furtherdiscussion.

[0065] After the patient is in the surgical position and the operativeportion of the spinal column is exposed, laminae and the facet joint andsurrounding tissues are removed in the amount necessary to provideexposure of the neurological elements and the intervertebral disc. Theintervertebral disc is excised (such as with a disk rongeur andcurrets), except for the anterior and lateral portion of the outerannulus. The excision is performed down to the sub-chondral bone of eachof the upper and lower vertebrae to encourage bone growth once theimplant is placed therein. Any removed bone can be kept for reuse asbone fragments as is explained in further detail hereinbelow. Attachedsoft tissue is removed from such removed bone and the bone is used as isor formed into smaller bone fragments for impaction into theintervertebral space.

[0066] The nerve root is retracted to allow access to the vertebral bodyand enable slots to be formed. The nerve root will be retracted toeither side at various times in the surgery. Advantageously, the boneimplant of the present invention is preferably slender (e.g., the height“H” is preferably greater than the thickness “T”), as discussed above.As a result, the nerve root does not have to be retracted very far.Thicker implants require that the nerve roots be pushed furtherlaterally. With larger lateral movement of the nerve root, more stressis placed on the root canal. This creates a higher risk of injury to thenerve root.

[0067] As mentioned, although the intervertebral disk is preferablysubstantially excised, a peripheral annulus fibrosis 34, hereinidentified as annulus 34, is left intact. The posterior annulus isremoved, but the anterior annulus remains as annulus 34. The annulus 34provides stability while the grafts in the intervertebral space arefusing. Annulus 34 acts as a tension band to hold the anterior portionof the vertebrae in a desired position. Annulus 34 also serves to holdbone fragments in place.

[0068] With reference now to FIGS. 4A-6B, an example of a method ofinsertion of implant 10 will be described in greater detail. As shown inFIGS. 4A and 4B, after initially removing the necessary tissues toexpose upper vertebrae 30 and lower vertebrae 32, and after removingsufficient tissue from therebetween, a first slot 36 and a second slot38 are formed in the vertebrae.

[0069]FIG. 4A demonstrates upper and lower slot portions 36A, 36B whichcombine to form a single slot 36 into which implant 10 is placed as willbe discussed in greater detail hereinafter. Upper and lower slotportions 38A, 38B combine to form another single slot 38 into whichanother implant is placed. Slot 36 depicts a formed slot, while thephantom lines of slot 38 depict the portions of the vertebrae wherecutting or impacting occurs to form the slot 38, as depicted in FIG. 4B.In a preferred embodiment, such slots are formed by forming upper andlower left slot portions 36A, 36B and upper and lower right slotportions 38A, 38B. The upper and lower slot portions together form acontiguous left slot 36 and a contiguous right slot 38.

[0070] To form the preferred upper and lower slot portions rectangular,angled slots are cut in the posterior portion of the respectivevertebra, also as depicted in FIG. 4b. In one embodiment, each slots iscontoured to extend from the posterior tip about one third to about onehalf of the length toward the anterior tip of the vertebrae. Thus, inone embodiment, the slots extend about one third to about one half ofthe length of the vertebrae, beginning at the posterior edge, asillustrated in FIG. 4B. Thus, in one embodiment, the slots do not extendpast approximately the center of the intervertebral space. However, itwill be appreciated that the slots may extend as short or as far as isrequired to achieve the desired distraction and lordosis with an implanttherein and an even longer or shorter slot may be created (e.g., throughthe use of cutting tools, impacting tools, and/or spacers) in anotherembodiment if properly configured. The cut out portion of the bone fromthe posterior vertebral body can be used as bone fragments to contributebone to the inner space, stimulate bone formation, and increasegraft-vertebral body contact.

[0071] Slots 36, 38 serve several functions. Also as depicted in FIG. 4Band 6C, the formed slots allow insertion of a rectangular block 10 ofbone while still maintaining lordosis. For example, the angled slots areformed in rectangular shape, which helps lock the implant in place.Also, the bone that is removed in forming the slot can be used in thesubsequent implant procedure as described hereinafter to help stimulatebone graft. As seen in FIGS. 4B and 4C, the slots are generally angledwith respect to a longitudinal axis “L” of the surfaces of the upper andlower vertebrae adjacent the invertebrael space. In addition, in theembodiment of FIGS. 4B and 4C, the anterior vertebral end-plates are notdisturbed, maintaining maximal anterior end-plate strength for fixationand distraction by the implant. For example, in one embodiment, byforcing the implants through the slots and further between thenon-slotted anterior portions of the adjacent upper and lower vertebrae,the anterior portions can be readily moved apart, thereby achievinglordosis upon compressing the posterior portions of the vertebrae, asshown in FIG. 6C. This dynamic will restore the normal anatomical curve,maintaining lordosis and allowing a proper fusion of the vertebral bone.

[0072] Cutting the slots also stimulates bone growth and the parallelsides of the slots provide surface area into which the posterior portionof the implant can grow. This growth stimulation and increase in surfacearea significantly encourages bone growth and proper fusion.

[0073] The vertebra shown in FIG. 4b preferably has a correspondingupper vertebra with corresponding slot portions. However, while it ispreferred to form a slot by forming upper and lower slot portions, asshown, it is also possible to implant implant 10 through the use of asingle slot portion in a single vertebra, e.g., as shown in FIG. 4b,with the other corresponding vertebra being unslotted. Thus, the term“slot” as used in this specification and the appended claims can includea slot formed from a single slot portion (e.g., upper or lower) and/or aslot formed from upper and lower slot portions, for example.

[0074]FIG. 4B shows a method of forming the slots with a tool entitled abox osteotome 50, according to the present invention. The head 57 (FIG.8a) of this instrument has a substantially rectangular cross sectionand, in one embodiment, cuts a box that substantially corresponds to thethickness of an implant 10. As illustrated in the lateral view in FIG.4B, the box osteotome 50 is placed on the posterior surface of thevertebrae, and a slot of the vertebrae is cut out. The cortical boneadjacent to the newly formed slot is left intact. The cut is from theposterior, angled towards the anterior to cut some of the cortical boneaway, leaving the remaining cortical bone.

[0075]FIG. 4C shows an impacting tool 60 according to another embodimentof the invention and features the formed slots in phantom lines. Unlikethe box osteotome 50, an implant impacting tool 60 does not cut into thebone. Rather, it can be used to form slots 36A, 36B, 38A, and 38B byindenting/crushing through and breaking away the bone. To indent thesurface of the bone, the implant impacting tool is positioned as shownin FIG. 4C with insertion member 64 positioned adjacent to the vertebralsurface that is inside the intervertebral space. An impacting member 62of tool 60 is positioned on the lateral surface of the vertebrae. Forceapplied to the impacting tool breaks away the cortical surface of thevertebrae. Underlying the cortical bone surface is softer cancellousbone, which can easily be indented or broken away. The bone that isimpacted or chipped off can be incorporated into the bone fusion as bonefragments.

[0076] The impacting tool 60 is particularly advantageous in that itprovides a measured depth for slots 36A, 36B, 38A, and 38B. Thisconfiguration allows effective control over the depth of slot desired.Different sizes of impacting tools are obtained by varying the depth ofimpacting member 62. For example, the impacting member 62 can be about4-6 mm in thickness, such that the slot is about 4-6 mm in depth,although a variety of other thicknesses and depths are available.

[0077] In one embodiment, as shown in FIG. 5A, following the formationof the upper and lower slot portions to form the respective slots, aspacer tool 70 is driven into each slot, thereby fine tuning theconfiguration of the intervertebral space 54, such as by increasing thesize of the slot. The spacer tool can create invertertebral space 54 foran implant through compression of cancellous bone in the upper and lowervertebrae and/or by distracting the upper and lower vertebrae. Spacertools 70 of various sizes can be used sequentially to obtain the desireddistraction of the intervertebral space 54 and the desired configurationof the slot. The tip of the spacer tool 70 can be shaped similarly tothe tapering nose section 14 of the implant 10 of the present invention,as shown.

[0078] In one embodiment, spacers are placed into the intervertebralspace 54 sequentially until the intervertebral space 54 achieves adesired height into which the implant fits. In one embodiment, a firstspacer tool smaller than the desired distraction size is first driveninto the intervertebral space to distract the intervertebral space to afirst distance. Subsequent spacer tools can then be sequentiallyinserted until the space reaches the desired distraction size. In otherwords, beginning with the small and progressing to larger sizes, theintervertebral spacers are sequentially inserted preparing the bed forthe implant until a intervertebral space is obtained according to what apre-operative X-ray suggests the implant should be placed in.

[0079] As shown in FIG. 5B, following the spacing shown in FIG. 5A, bonefragments are preferably placed into the intervertebral space 54. Thebone fragments serve the dual purposes of supplying support andstability to the bone implant and vertebral column during fusions andgrowing and incorporating into the bone fusion. It is desireable to fillthe entire intervertebral space 54 with bone comprising fragments andimplants. For example, following the initial distraction with the spacertool, bone fragments from the lamina and facet joints can be ground intosmaller fragments and placed in the intervertebral space. The term “bonefragments”, however, as used throughout this specification and theappended claims shall include any bone material that is capable of beingfit into the intervertebral space, such as bone chips, bone pulp, orother fragments of bone, for example.

[0080] A sufficient quantity of bone fragments are placed in theintervertebral space to surround the implant and fill the spacefollowing impacting as described hereinafter. This ensures bone growththroughout the space as well as adequate support and stability. Afterpacking the intervertebral space with bone fragments, spacer tools 70can be reinserted, as shown in FIG. 5C to impact and spread the graftand create a space for the implant. The process of filling in theintervertebral space with bone fragments, then placing the spacertherein can be continued until the space if filled with fragments butretains a space for the implants, as illustrated in FIG. 6B.

[0081] Additional bone fragments can be obtained, for example from theiliac crest bone or any extra bone obtained from the spinus or facetsduring other stages of the surgery. One of skill in the art willappreciate in light of the disclosure herein that materials areregularly developed and may serve as adequate “bone fragments” of thepresent invention, provided they function to promote bone fusion andprovide the requisite strength. For example, a bone morphogenic proteinmay provide a suitable material to serve as “bone fragments” of thepresent invention.

[0082] With reference now to FIG. 6A, following the placement of thebone fragments into the slot, each implant is preferably driven intoeach slot 36, 38 through the use of an implant impactor 90. The implantimpactor 90 has a rectangular shape that substantially corresponds withthe proximal, posterior surface 21 of implant 10 and substantiallycorresponds to the size of the slot into which the implant is to beplaced. The rectangular tip has a plurality of spikes 92 to ensure itdoes not slip off the implant during impacting.

[0083] In one embodiment, implant 10 is driven past the location of theslot and adjacent the anterior annulus 34, as shown in FIGS. 6b and 6C.The implant is placed in the intervertebral space and aligned with thecorresponding slot. The implant is then impacted into the space and, inone embodiment, is seated 2 mm to 3 mm past the posterior vertebral bodycortex of the adjacent vertebra. For example, in one embodiment, thedistal tip of the implant 10 is driven approximately 3 mm from thedistal tip of annulus 34, while the proximal tip of implant 10 isapproximately 2-3 mm from the proximal end of the intervertebral space.

[0084] In the case of multiple disc replacements, the procedure isrepeated for all intervertebral spaces on one side before going to theother side. Patients with scoliosis can be treated by inserting animplant only on the concave side with bone fragments filling the spaceon the convex space side. As illustrated in FIG. 6B, the bone fragments80 are compacted in the intervertebral space and spread around theimplant 10. In addition, as shown in FIG. 6C, upon placing implant 10far enough into the intervertebral space, annulus 34 tightens and theanterior portions of the vertebrae distract.

[0085] With continued reference now to FIG. 6B, an overhead view of anexample of first and second implants driven into first and secondrespective slots 36, 38 is shown. As shown, implants 10A, 10B are drivenbetween neighboring discs such that a balance is achieved fosteringproper distraction and fusion.

[0086] Upon driving implant 10 into the desired space, lordosis ismaintained in a desired amount by mechanically compressing the posteriorportions of the vertebrae, and maintaining the vertebrae in thecompressed position, such as through the use of a mechanical fixationdevice 110, as depicted in FIG. 6C.

[0087] For example, after the implantation is complete, the vertebralcolumn can be mechanically fixed in position with screws to obtain thedesired lordosis as discussed in U.S. Pat. Nos. 5,947,965 to Bryanentitled SPINAL FIXATION APPARATUS AND METHOD, 5,676,665 to Bryanentitled SPINAL FIXATION APPARATUS AND METHOD, 5,498,262 to Bryanentitled SPINAL FIXATION APPARATUS AND METHOD, and 5,306,275 to Bryanentitled LUMBAR SPINE FIXATION APPARATUS AND METHOD, the disclosures ofeach of which are incorporated herein by reference. In one embodiment, aportion of the pedical screw procedure is started before the implant isimplanted, after which the procedure is completed. For example, forconvenience pedical pins (placed preliminary to placing screws) may beplaced in the positions desired while the practitioner is working on aparticular side of the intervertebral space before implantation. Thescrews may then be placed in the desired positions followingimplantation, for example. Optionally, no pedical pins are usedpreliminary to the use of screws.

[0088] The mechanical fixation devices may optionally be removed at anytime after the fusion is complete, but such removal is not necessarilyrequired.

[0089] With reference now to FIG. 7a, upon tightening the mechanicalfixation device 110, the posterior portions of the upper and lowervertebra are compressed, thereby increasing the tension in annulus 34and maintaining a desired level of lordosis. With reference now to FIG.7b, following a certain amount of time, the upper and lower vertebraefuse together and the bone fragments and implanted implants fuse,thereby forming a solid bone member 100. Bone member 100 has receivedfusion at three levels (i.e., three intervertebral spaces fused), withan upper disk 102 remaining. The solid bone member is now free fromdisruptive, herniated, or injured discs, is convenient and practical fora patient, and often delivers the patient from significant pain withoutimmobilizing or significantly reducing the mobility of the patient.Despite the slight loss of spinal flexibility due to the spinal fusion,a patient's overall mobility is often not significantly impaired. Thisis due to the relatively small import of the spinal column relative tothe hip and other joints in overall flexibility.

[0090] Referring now to FIGS. 8A-9, the present invention alsoencompasses a variety of instruments used to implant the intervertebralimplant discussed hereinabove. The box osteotome 50 discussedhereinabove may be structured as illustrated in FIGS. 8A and 8D. It iscomprised of a handle 55, a neck 56 coupled to handle 55, and a head 57coupled to neck 56. Head 57 comprises a scraper having first and secondlongitudinally extending side members 58 a, 58 b that coupletransversely to a longitudinally extending body member 59. The distaledges of the longitudinally extending members 58 a, 58 b, and 59 can besharpened to facilitate cutting upper and lower slot portions. Inanother embodiment, the edges are blunt, thereby assisting in crushingthe bone. The thickness of body member 59, and consequently the distancebetween side members 58 a and 58 b may correspond generally to thethickness of implant 10, thereby cutting the desired slot configured tofit the implant therewithin. Thus in one embodiment, head 57substantially corresponds to the thickness of the implant (i.e., hassubstantially the same thickness as the implant).

[0091] Head 57 has a substantially rectangular cross section. Head 57 isconfigured to form a rectangular slot. In one embodiment, head 57extends slightly outwardly as it moves away from the neck portion. Head57 is configured to cut portions of the posterior portion of the boneaway and/or to crush portions of the posterior bone.

[0092] As mentioned above, alternatively, slots 36, 38 can be formed bycrushing or impacting rather than cutting. Referring to FIGS. 8B, 8E, animpacting instrument 60 of the present invention is comprised of ahandle 62, a neck 68 coupled to the handle 62, and a head 69 coupled toneck 68. As illustrated in FIG. 8E, head portion 69 of impactinginstrument 60 is comprised of an impacting member 62 and an insertionmember 64 perpendicular to said impacting member 62. To indent thesurface of the bone, the impacting instrument is position as shown inFIG. 4C with insertion member 64 positioned adjacent to the vertebralsurface that is inside the intervertebral space. The impacting member 62is positioned on the posterior surface of the vertebrae. Force appliedto the impacting instrument 60 breaks away the cortical surface of thevertebrae. Underlying the cortical bone surface is softer cancerousbone, which can also easily be indented or broken away.

[0093] This configuration of impacting instrument 60 allows effectivecontrol over the depth of slot desired, as discussed above. Differentsizes of impacting instruments are obtained by varying the depth ofimpacting member 62. For example, the impacting member 62 can be 4-6 mmin depth, although a variety of other configurations and sizes areavailable.

[0094] As seen in FIG. 8F, in an alternative embodiment of an impactorhead 60 a, the head comprise an insertion member 64 a and an impactingmember 62 a having a sharpened lip that can also be used for cutting.

[0095] Referring now to FIGS. 8C and 8G, an implant impactor 90according to the present invention is comprised of a handle 94, a neck96 coupled to handle 94, and a head 98 coupled to neck 96. Asillustrated in FIG. 8G, head portion 98 of the impacting instrument 90has a generally rectangular shape and a plurality of spikes 92 thereon.Optionally, corrugations or grooves 93 may be substituted for spikes asshown in the alternative head 98 a of an implant impactor 90 a, shown inFIG. 8H. Implant impactor 90 is used to force implant 10 into slots 36,38 formed in the vertebrae. Spikes 92, corrugations, or grooves 93assist in gripping implant 10 as it is being forced into the slots. Suchspikes 92, grooves 93 or corrugations are examples of means forenhancing the gripping surfaces of the heads. One skilled in the artwill recognize, in light of the disclosure herein, that other grippingmeans can be employed to grip the implant.

[0096] In one embodiment, head 98 of impactor 90 substantiallycorresponds to the height and thickness of implant 10 (i.e., has asubstantially similar height and thickness), such that impactor 90 caneffectively force implant 10 through a slot substantially correspondingto the height and thickness of the implant without creating a largerslot.

[0097] Referring now to FIG. 9, spacing instruments 70, 72, 73, and 75are each comprised of a handle 130, a neck 132 coupled to the handle,and a head 134 coupled to the neck 132. The head portion 134 has a bodyportion 136 and a nose section 138 tapering inwardly and distally awayfrom the body portion to form a generally pointed or rounded tip portionat a distal end thereof, substantially similar to implant 10. As isillustrated in the figures, the head portion 134 of each spacinginstrument has a different thickness.

[0098] The spacers can thus be used sequentially to distract adjacentvertebrae and increase the height of the slots 36, 38. In oneembodiment, the head of the final spacing tool used in the sequence isslightly smaller than the implant, such as about 2 mm smaller in heightthan the height “H” of the implant, for example, such that the spacerssubstantially create a space for the implant, but such that the implantis press fit in a tightfitting relationship between the adjacentvertebrae.

[0099] Nevertheless, as shown in the tools of FIG. 9, in one embodiment,even if the head of the spacer is slightly smaller, the spacer still hasa shape substantially similar to the implant such that the spacercreates a space sufficient for the implant to be implanted into.

[0100] In one embodiment, the spacers can crush some of the cancellousbone in the intervertebral space, such as in the posterior portionand/or approximately the middle of the intervertebral space (and even inthe anterior portion in certain embodiments), thus fine tuning the slotin the intervertebral space. In one embodiment, the implant is pressedpast the middle of the intervertebral space, press fitting into thecancellous bone in the space and contacting the anterior, cortical boneand thereby distracting, i.e., pushing apart the anterior peripheralportions of the adjacent vertebrae.

[0101] The instruments described in FIGS. 8 and 9 may be manipulated ina variety of different manners, such as by being held by a practitionerand/or contacted with a mallet or hammer, for example, to derive theforce necessary to perform a particular procedure, as will beappreciated by one skilled in the art in light of the disclosure herein.

[0102] Another aspect of this invention is a system including one ormore of the hereinabove described instruments, one or more vertebralimplants 10, and, optionally one or more bone fragments.

[0103] The following example is given to illustrate one possibleembodiment of the present invention, and is not intended to limit thescope of the invention.

EXAMPLE 1

[0104] The following procedure was effectively performed on a patient. Amidline incision was made and the patient's spine was exposed bysubperiosal dissection. Decompression was begun with partial facet jointexcision. The capsule of the facet joint was removed with electriccautery and periostial elevator. Since virtually all removed bone ispreferably used as graft, extra time was taken to meticulously removeattached soft tissue. The upper facet was cut transversally with anosteotome and removed. Initially, the spinous processes were left intactto facilitate distraction with the laminus spreader.

[0105] The interspinous ligament was removed and a laminae spreader wasinserted. Cartilage and other soft tissue from the facet joint wereremoved with a cob elevator and an adison rongeur. The inferior facetwas excised, saving the small bits of bone for later grafting. The diskspace was radically excised to the outer annulus. The end-plates werevigorously curetted to bone. A cottonoid was placed, the laminaespreaders removed, and the decompression procedure was performed at eachof the other levels for which fusion was desired, all on the same side.

[0106] The transverse process was cleaned of soft tissue and thetransverse process retractor was placed. Sleeves of the pedicle burrwere placed over the transverse process and the pedicle entry point wasburred. A small diameter pedicle reamer was placed in the burr craterand pushed down the pedicle with back and forth motions. A larger reamerwas then inserted.

[0107] A C-clamp trial confirmed the C-clamp would fit close to bonelateral to the facet joint. The superior facet joint (i.e., the portionabove the level of the fusion) was not violated. A pedicle pin wasinserted. The inferior pedicles were reamed under direct vision. Themedial wall was palpated with a nerve hook. Burring and reaming wereperformed in the usual manner. After inserting the reamer and the pins,repeat palpation with the nerve hook confirmed correct pedicle reaming.

[0108] Burring, reaming and pin insertion were accomplished on the sameside for the remaining pedicles to be instrumented. The same procedurewas then performed on the other side.

[0109] After all levels had been decompressed and pedicle pins placed,the laminus spreader was reinserted and the nerve roots retracted.Notches were cut in the posterior portion of each vertebral body.Beginning with a small height and progressing to larger heights, theintervertebral disk spacers were sequentially inserted preparing the bedfor the implant. Bone from the lamina and facets were ground into bonemeal and placed in the disk space. Spacers were reinserted to impact thebone and recreate the bed for the implant.

[0110] The implant was impacted into the space and seated two to threemillimeters below the posterior vertebral body cortex. The procedure wasrepeated for all disk spaces on one side before going to the other side.(Patients with scoliosis can be treated by inserting a implant on theconcave side, and bone fragments only on the convex side.)

[0111] A final inspection of the spinal canal and nerve roots wasperformed. The foot of the bed was elevated to assist in restoration oflordosis prior to instrumentation. Instrumentation began with the upperpedicle. A depth gauge was inserted to palpate the pedicle wall anddetermine the screw length. A construct comprising an L-rod held with alocked stem clamp, other stem clamps as needed and a C-clamp with aC-clamp holder was assembled. The measured pedicle screw was insertedthrough the C-clamp and placed into the pedicle. The C-clamp was pusheddown to its final resting position close to bone and lateral to thefacet.

[0112] The screw was then inserted. The screw was tightened to preventmedial/lateral translation, but not rotation of the L-rod on theC-clamp. The upper facet joint was not disturbed. A C-clamp was thenplaced on the inferior stem clamp, the stem clamp holder was removed,the pin in the pedicle was removed and reinserted through the C-clampand down into the pedicle. The pin was then removed, the depth gaugemeasurement to the anterior cortex of the sacrum was obtained, and thenthe screw was inserted. The screw could then perfectly engage theanterior cortex of the sacrum, obtaining bi-cortical fixation withoutneed for x-raying.

[0113] Lordosis can be increased by shortening the distance between theupper and lower screws producing normal, physiological extension withvertebral rotation. The superior and inferior screws were loosened andan upper stem clamp was secured to the rod by tightening the screw.Compression was applied between the stem clamps and the bottom stemclamp screw was tightened. The upper and lower screws were thentightened to lock the construct into its final position.

[0114] Another method of restoring lordosis is to use angled lordodicrods. The rods can be placed in the superior and inferior screws,compressed together and the inferior stem clamp screw can then betightened. The middle pedicle screws can then be inserted easilyregardless of pedicle orientation.

[0115] Cross-plates were then applied. These could be applied atmultiple levels without the need for added connectors to the rod. Afinal tightening of all screws was then performed. An iliac crest bonegraft was obtained by raising a skin-and-subcutaneous-flap over theright ileum. This bone was harvested and then packed under directdivision along the transverse processes and the lateral wall of thepedicles. Any extra bone obtained from spinus processes or facets wasground into a mesh and impacted laterally. A final inspection of thespinal canal and nerve roots was then accomplished. The wound was closedin the usual manner, and prophylactic antibiotics were administered for48 hours. An abdominal binder was used. No rigid brace was required.

[0116] This example illustrates one embodiment of the present inventionalthough a variety of other procedures and methods can be employedaccording to the present invention Embodiments of the present inventionare also disclosed in copending U.S. Patent Applications entitled“Spinal Vertebral Implant” to Donald W. Bryan, filed Sep. 15, 2000,which is incorporated herein by reference and “Instruments for InsertingSpinal Vertebral Implant” to Donald W. Bryan, filed Sep. 15, 2000, whichis incorporated herein by reference.

[0117] The present invention may be embodied in other specific formswithout departing from its spirit or essential characteristics. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which comes within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed and desired to be secured by United States LettersPatent is:
 1. A method for placing an implant between first and secondvertebrae pursuant to a spinal surgical procedure, the methodcomprising: (a) providing a spinal vertebral implant configured tofoster bone fusion between upper and lower adjacent spinal vertebraebetween which the implant is placed pursuant to a spinal surgicalprocedure; (b) forming at least one slot in at least one of the upperand lower vertebrae; and (c) inserting the implant into the slot suchthat the implant is maintained between the upper and lower vertebrae. 2.A method as recited in claim 1, wherein the implant comprises asubstantially rectangular base and a tapering nose extending integrallyfrom the base.
 3. A method as recited in claim 1, wherein the slotcomprises an upper slot portion.
 4. A method as recited in claim 1,wherein the slot comprises a lower slot portion.
 5. A method as recitedin claim 1, wherein the slot comprises an upper slot portion and a lowerslot portion.
 6. A method as recited in claim 1, wherein the slot isgenerally angled with respect to a longitudinal axis of the surfaces ofthe upper and lower vertebrae adjacent a space between the vertebrae. 7.A method as recited in claim 1, wherein the slot extends from theposterior ends of the vertebrae at least approximately one third toapproximately one half the distance between the anterior and posteriorends of the upper and lower vertebrae, and wherein the implant isinserted into the slot.
 8. A method as recited in claim 7, wherein theanterior edges of the upper and lower vertebra are unslotted.
 9. Amethod as recited in claim 8, wherein the implant is inserted betweenthe upper and lower slot portions and further into an anterior portionof a space between the vertebrae that is unslotted.
 10. A method asrecited in claim 1, wherein the slot extends from the posterior ends ofthe vertebrae no further than approximately one third to approximatelyone half the distance between the anterior and posterior ends of theupper and lower vertebrae, and wherein the implant is inserted throughthe slot.
 11. A method as recited in claim 1, further comprisingcompressing the posterior portions of the vertebrae following insertionof the implant, thereby achieving a desired level of lordosis.
 12. Amethod as recited in claim 1, wherein the method further comprisesplacing bone fragments within a space between the upper and lowervertebrae.
 13. A method as recited in claim 1, wherein the implant isplaced in a tight fitting relationship between the vertebrae.
 14. Amethod as recited in claim 1, wherein the implant has a convex side, andwherein the convex side faces medially and a concave side faceslaterally following insertion of the implant.
 15. A method for preparingupper and lower adjacent vertebrae to receive a spinal vertebral implanttherebetween, the spinal vertebral implant configured to foster bonefusion between the upper and lower adjacent spinal vertebrae, the methodcomprising: removing a substantial portion of an intervertebral diskextending between the vertebrae; and forming upper and lower slotportions in respective upper and lower vertebrae to form a collectiveslot, the slot configured to receive an implant therein.
 16. A method asrecited in claim 15, wherein each slot portion is angled with respect toa longitudinal axis of a respective upper and lower vertebrae.
 17. Amethod as recited in claim 15, wherein forming a slot comprises placingsequentially sized spacers between the vertebrae.
 18. A method asrecited in claim 15, wherein forming the slot comprises a methodselected from the group consisting of: (i) cutting through an outercortical bone layer of the posterior portion of said upper and lowervertebrae; and (ii) impacting the outer cortical bone layer of theposterior portion of said upper and lower vertebrae.
 19. A method forplacing first and second implants between first and second spinalvertebrae from which a substantial portion of an intervertebral diskextending between the vertebrae has been removed, the method comprising:(1) providing first and second spinal vertebral implants, each implantconfigured to foster bone fusion between upper and lower adjacent spinalvertebrae between which the implant is placed pursuant to a spinalsurgical procedure; (2) forming first and second slots in at least oneof the upper and lower vertebrae; and (3) inserting the first and secondimplants into respective first and second slots, such that the implantsare mounted between the upper and lower vertebrae.
 20. A method forplacing an implant between first and second vertebrae from which asubstantial portion of an intervertebral disk extending between thevertebrae has been removed, the method comprising: (1) providing aspinal vertebral implant configured to foster bone fusion between upperand lower adjacent spinal vertebrae between which the implant is placedpursuant to a spinal surgical procedure, the spinal implant comprising asubstantially rectangular shaped base; (2) providing a first slotportion in an upper vertebra and a second slot portion in a lowervertebra to form a collective slot, the collective slot configured toreceive the implant therein; and (3) inserting the implant into thecollective slot between the upper and lower vertebrae.